Method and apparatus for producing coated flat glass

ABSTRACT

A concentration of elemental metal is built up in a glass surface by subjecting the glass, at a suitable elevated temperature, to ion exchange and ion reduction treatments alternately. The ion exchange may be effected electrolytically or by vapor deposition, and the ion reduction may be effected by exposing the glass surface to a reducing atmosphere.

United States Patent 1 1 3,622,295

721 Inventors Da id rd un -s; 501 Field of Search 65/30. 60. i li RamseyMlltmln. both of Pr co 99 A, 182 R; 204/300, 180 R; 161/1 1 17/124 cEngland 211 Appl. No. 839,248 References Cited 22] Filed July 7, 1969 vUNITED STATES PATENTS I 1 Pmmed 3 467 s 9 1969 L 1 t' 1. 30 1 Assign" W11mm 3:505:048 41970 PILLS? 65130 W Lanmhire, 3,429,742 2 1969 Grego613i. ll7/l2A I 1 Prlomy 1 0 5 3,479,217 11 1969 Spanoudis 117/124 x[33] Great Britain 4 I [31 33,676/68 Primary Exammer- Reuben Fnedman[54] METHOD AND APPARATUS FOR PRODUCING COATED FLAT GLASS 13 Claims, 3Drawing Figs.

(52] US. Cl 65/30, 65/99 A, 65/l82 R, l17/l24 C. 204/ R, 204/300 511Int. Cl ..C03c 17/00,

Assistant Examiner-Robert L. Lindsay Atrorne vMorrison, Kennedy &Campbell ABSTRACT: A concentration of elemental metal is built up in aglass surface by subjecting the glass, at a suitable elevatedtemperature, to ion exchange and ion reduction treatments alternatelyThe ion exchange may be effected electrolytically or by vapordeposition, and the ion reduction may be effected by exposing the glasssurface to a reducing atmosphere.

PATENTEDNUV 2 3 I971 SHEET 1 OF 2 lnvenlom DAVID GORDON LOUKES andWILLIAM RAMSEY MALTMAN mm, A

METHOD AND APPARATUS FOR PRODUCING COATED FLAT GLASS BACKGROUND OF THEINVENTION This invention relates to the manufacture of glass, andspecifically to the manufacture of glass with a desired concentration ofelemental metal in its surface.

Metal can be introduced into glass by electrolytic processes, and bymigration of metal ions into the glass at high temperature in a reducingatmosphere. Metal ions which have migrated into the glass aresubsequently reduced to the metallic state.

It is sometimes desirable to achieve a very high concentration ofelemental metal in the glass surface, for example when making a highlyreflective layer. Hitherto the concentration of elemental metal whichcan be introduced into the glass surface has been detennined by theionic concentration of mobile cations in the original glass surface.

It is a main object of the present invention to provide a method andapparatus whereby the concentration of elemental metal introduced intothe glass surface, is built up to several times the ionic concentrationof the original mobile cations in the untreated glass.

SUMMARY According to the present invention a method of manufacturingglass having a desired concentration of elemental metal in its surface,comprises subjecting the glass, at a temperature at which it issusceptible to surface modification, to surface treatment by causingmetal ions to enter the glass surface followed immediately by reductionof the metal ions to the elemental metal, and repeating such surfacetreatment successively with the same or different metals to build up adesired concentration of elemental metal in the glass surface.

.Each combination of ion exchange and reduction steps introduces arelatively small proportion of metal into the glass surface andreduction of the metal ions introduced at each step takes place whilethose ions are close to the glass surface.

According to one embodiment of the invention the metal ions are causedto enter the glass electrolytically from a molten metal body in contactwith the glass surface by passing an electric current between the moltenmetal body and the glass surface, which molten metal body acts as ananode of the electrolytic circuit.

The molten metal body preferably clings to a metal-locating member towhich the current is supplied. The molten metal body may cling to ametal bar which is soluble in the molten metal body.

In one embodiment of the invention the molten metal body is movedrepetitively over each region of the surface of the glass to be treated,reduction of the metal ions in the glass surface being effected byexposing the said surface to a reducing atmosphere between successivepassages of the anode over each respective surface region.

Alternatively, the glass may be moved past an anode structure comprisinga plurality of molten metal bodies contacting the glass and constitutingmolten metal anodes spaced apart in the direction of glass movement, thespaces between adjacent anodes containing a reducing atmosphere.

This latter method is particularly applicable to the manufacture of flatglass in the form of a continuous ribbon, and the invention can also beapplied to the manufacture of float glass in which a ribbon of glass isadvanced along a bath of molten metal. From this aspect the inventionprovides a method of manufacturing float glass having a desiredconcentration of elemental metal in one face of the glass, comprisingadvancing float glass in ribbon form along a bath of molten metal,contacting the upper face of the glass with a plurality of molten metalbodies extending transversely of the ribbon of glass, which bodies arespaced apart in the direction of advance of the glass, and exposing theupper face of the glass to a reducing atmosphere in the spaces betweenthe molten metal bodies.

The ions may alternatively be introduced into the glass by ion exchangefrom the vapor phase.

The invention further provides apparatus for use in the manufacture ofglass by the above-defined method, said apparatus comprising means forsupporting glass to be treated at a temperature at which the glass issusceptible to surface modification, an anode including a body of moltenmetal to be introduced into the glass, which body has a surface inelectrical contact with a surface of the glass, an electrical currentsource connected to the anode and arranged to pass an electrolyticcurrent into a surface of the glass from said molten metal body, meansconfining a reducing atmosphere over said surface of the glass, andmeans for effecting relative movement between the glass and the anodestructure in such a way that each surface region of the glass issubjected to a succession of electrolytic surface treatments by saidmolten metal, alternating with ion reduction treatments by the reducingatmosphere.

In one embodiment of the invention for use in the manufacture of flatglass in ribbon form, the support means comprises means permittingadvance of the glass in ribbon form at a controlled rate successivelypast a plurality of said anodes spaced apart in the direction of advanceof the ribbon, the spaces between successive anodes being filled with areducing atmosphere.

Further the invention provides apparatus for use in the manufacture offloat glass which is advanced in ribbon form along a bath of moltenmetal, wherein the anodes are mounted above the bath surface so that themolten metal bodies contact the upper face of the glass, and the bath isconnected to the electrical current source so as to act as the cathodefor electrolytic treatment of the glass as it passes beneath the moltenmetal bodies.

For use in the surface treatment of a glass article, the apparatus maycomprise a molten metal support for the article and means for moving theanode cyclically over a surface of the article so that each surfaceregion is swept repetitively thereby.

The invention also comprehends glass having a concentration of elementalmetal in its surface, produced by a method as defined above.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic longitudinalvertical section through an apparatus according to one embodiment of theinvention,

FIG. 2 is a diagrammatic perspective view on an enlarged scale of theanode structure employed in the apparatus of FIG. I, with the hoodstructure removed, and

FIG. 3 is a diagrammatic cross-sectional view of an apparatus fortreating glass articles in accordance with another embodiment of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. I, aforehearth of a continuous glass melting furnace is indicated at l and aregulating tweel at 2. The forehearth 1 ends in a spout 3 comprising alip 4 and side jambs 5, one only of which is shown in FIG. 1.

The spout 3, which has a generally rectangular cross section, isdisposed above the floor 6 of an elongated tank structure havingintegral end walls 7 and 8 at the inlet and outlet ends of the tankrespectively. The tank structure holds a bath of molten metal 10comprising, for example, molten tin or an alloy in which tinpredominates, the bath having a specific gravity greater than that ofglass.

A roof 11 having depending sidewalls 12 (one only of which is shown) andintegral depending end walls I4, 15 at the inlet and outlet endsrespectively of the bath is supported over the tank structure. The inletand outlet end walls I4, l5 respectively define inlets and outlets l6,17 for the glass, the outlet 17 being located above the surface of thebath. Driven rollers 18 are arranged externally of the outlet 17 toguide the ultimate ribbon of glass formed on the bath through the outlet17. The rollers convey the glass ribbon to an annealing lehr in awell-known manner, and also apply a tractive effect to the ribbon todraw it along the bath in the direction of the arrow A.

Molten soda/lime/silica glass is poured over the spout 3 on to themolten metal bath 10, the rate of flow of the molten glass beingregulated by the tweel 2. in falling from the spout 3 the molten glasshas a free fall of a few inches, exaggerated in F 1G. 1, on to thesurface of the bath 10. This free fall is such as to ensure theformation of a heel 21 of molten glass behind the glass 20 pouring overthe spout 3, which heel 21 extends up to the inlet end wall 7 of thetank structure.

The temperature of the molten glass is regulated by thermal regulators22, 23 disposed in the molten metal bath 10 and in the headspace overthe bath respectively so as to ensure that a layer of molten glass 24 isestablished in the surface of the bath 10. As this layer 24 advancesfrom the inlet 16 in the direction of arrow A there is lateral flow ofthe glass under the influence of surface tension and gravity so that abuoyant ribbon 25 is developed as the limit of this free flow, the widthof the tank structure being such as not to impede this lateral flow.

A protective gas, for example nitrogen or another inert gas, is suppliedto the headspace over the bath 10 through ducts 26 which are provided atintervals in the roof 1]. Thus a plenum of protective gas is maintainedin this headspace, with a continuous outward flow of protective gaspassing through the inlet 16 and outlet 17.

At a region of the bath 10 where the glass ribbon 25 is at asufficiently high temperature to be susceptible to surface modification,a hood structure 27 is disposed in the bath headspace. the hoodstructure 27 leaving an open lower end which is disposed in closejuxtaposition to the surface of the bath 10, so that the interior of thehood structure 27 is for practical purposes substantially isolated fromthe remainder of the bath headspace. A conduit 28 communicates with theinterior of the hood structure 27 and extends outwardly of the roof 11to a source (not shown) of a reducing gas, conveniently hydrogen. Thereducing gas may be supplied to the interior of the hood structure 27either alone or in admixture with an inert gas such as nitrogen. Thehood structure 27 is elongated in the direction A of ribbon advance andextends transversely across the entire width of the glass ribbon 25.

An anode structure 30 is mounted within the hood structure 25 andcomprises (FIG. 2) an array of elongated parallel metallic anode members31 extending transversely across the ribbon 25 and parallel to thesurface thereof. Each anode member 31 has a lower face 32 which isparallel to and closely spaced from the surface of the ribbon 25. Toeach lower face 32 clings a molten metal body 33 which constitutes amolten metal anode and which makes electrical contact with the upperface of the glass ribbon 25.

The anode members 31 are connected individually, or, as shown in FIG. 1,collectively, to the positive terminal of a direct current electricalsource 34, the negative terminal of which is connected. as showndiagrammatically in FIG. 1, to the metal bath 10.

At the temperature of the surface treatment of the glass, which istypically of the order of 750 C., the glass is electrically conductiveand constitutes in effect the electrolyte of an electrolytic circuit.Metallic ions enter the upper surface of the glass ribbon 25 from themolten metal bodies 33 to modify the glass characteristics. It isthought that the metal ions enter the glass as a result of ion exchangewith sodium ions in the glass.

Each anode member 31 is very narrow, so that each molten body 33clinging to its anode member 31 has a very small extent in the directionof glass ribbon advance, A. Typically, for a rate of ribbon advance of150 inches per minute, each anode member 31 may extend A; inch in thedirection of ribbon advance, the anode members 31 being regularly spacedat intervals of 2 inches.

Because each of the anodes constituted by the molten metal bodies 33introduce only a small fraction of the total quantity of the metal ionswhich enter the glass, the depth to which metal ions are driven into theglass surface, as it passes beneath any one of the anodes is very small.The reducing atmosphere which diffuses into the glass in each interanodespace reduces to the metallic state substantially all of the metal ionsintroduced into the glass from the last molten anode 33, before ions candiffuse deeper into the glass. This results in a concentration ofelemental metal in the surface of the glass, which concentration buildsup as the glass passes beneath the successive molten anode bodies,because the elemental metal in the metal enriched surface cannot diffusein the glass, and it therefore remains in or close to the surface of theglass ribbon as further migrations of metal ions are imposed into themetal enriched surface region of the glass and as each influx of ions isreduced. For example, where the molten metal bodies are copper/bismuthalloy, and the reducing atmosphere is hydrogen, copper ions enter theglass and the reduction process may be represented by:

The resulting hydrogen ions in the glass undergo ion replacement bycopper ions driven into the glass surface by electrolytic action fromthe next of the molten bodies 33. The hydrogen ions are driven moredeeply into the body of the glass, and cations, e.g., sodium ions aredriven out of the glass at the interface with the molten metal bathwhich acts as the cathode. Copper ions newly introduced into the glasssurface are then reduced to the metallic state as soon as the glasssurface passes from beneath the molten body 33. There is thus a releaseof elemental copper particles in the extreme surface layer of the glassand the concentration of copper metal'in the glass surface as a resultof the repetitive treatment is several times greater than the ionicconcentration of the original mobile cations in the glass surface.

It will be appreciated that by using the anode structure 30 describedabove the advancing glass ribbon 25 is subjected to a succession ofelectrolytic ion-exchange steps (at each electrode member 31)alternating with ion-reduction steps (between adjacent pairs ofelectrode members 31 In effect, the buildup of ions in the glass surfacetakes place in a series of short steps or pulses, each followed by anionreduction step to give the elemental metal. Consequently, a layer ofthe elemental metal builds up in or close to the upper surface of theglass ribbon 25. The concentration of metal in this surface layerdepends on the number of times the ion-exchange/ion reduction sequenceof operations is repeated-that is, on the number of anode members 31(and clinging molten metal bodies 33) in the anode structure 30.

The number of anode members 31 is exaggeratedly small in F I08. 1 and 2for ease of illustration. in practice the number of anode members 31would typically be of the order of 50.

Two examples of electrolytic processes using the apparatus of F 16$. 1and 2 are given below:

EXAMPLE 1 An anode structure 30 comprising 50 anode members 31 is used,each anode member comprising a copper bar having a wetted surface 32which is :-inch long in the direction A of ribbon advance. The anodemembers 31 are regularly spaced apart at 2-inch intervals and the glassribbon, which is lOO inches wide, is advanced at a speed of I50 inchesper minute. The treatment is effected with the glass at a temperature ofabout 750 C. using a current of 50 amps (i.e., 1 amp per anode member31) and a reducing atmosphere containing a high concentration ofhydrogen. The resulting glass ribbon had a layer of metallic copper inits surface displaying a reflectivity of about 50 percent.

EXAMPLE II An anode structure 30 comprising 30 anode members 31 isarranged in a region of the bath where the glass temperature is about700 C. Each anode member 31 comprises a copper bar 0.l25-inch thick,with its thickness extending in the direction of ribbon advance A, theseparation between adjacent anode members 31 being equal to the distancetravelled by the ribbon 25 in l secondthat is, 2 inches for a rate ofribbon advance of 120 inches per minute. Each anode member 31 isarranged to pass an electrolytic current of 50 milliamps per 1.5 inchesof width in a direction transverse to the direction of ribbon advance(i.e., along the width of the ribbon). The reducing atmosphere comprisesa mixture of 50 percent hydrogen and 50 percent nitrogen.

In both the examples described above, metallic copper is introduced intothe glass surface. A similar technique can be used for introducing otherreducible metallic ions into the glass.

The molten metal body 33 clinging to each anode member 31 may be analloy consisting of an inert solvent metal e.g., bismuth, and a highermelting point metal e.g., copper or silver. The anode members 31 towhich the molten bodies 33 cling are made of the pure high melting pointmetal e.g., copper or silver. With this arrangement the high meltingpoint constituent of the alloy is continuously replenished bydissolution of the anode members at the same rate as the high meltingpoint metal is being consumed from the molten bodies in treating theglass.

The metal dissolved by the bodies 33 enters the glass under theinfluence of the applied electric field, following ion exchange withsodium ions in the glass, as described previously. As anode metal isremoved from the molten bodies 33 and enters the glass, more metal isdissolved by the bodies 33 from the anode members 31 to maintain anequilibrium concentration of the metal in the molten alloy bodies 33.Each molten body 33 therefore acts as an effective bufier" between therespective anode member 31 and the glass ribbon 25.

To assist the wetting of a copper anode 31 by a molten body 33 ofbismuth a small proportion of lead (about 2 percent) may be added to thebody 33.

Since the amount of molten material in each body 33 is small, and thismaterial clings to the respective anode member 31. the anode structure30 can be disposed in regions where the glass temperature is as high as950 C. without causing distortion of the glass surface.

When the molten anodes are constituted by a low melting point metal e.g., lead, the anode members may be made of, or faced with, an insolublehigh melting point metal such as ruthenium. Lead is added to the moltenbodies 33 to compensate for the metal consumed in treating the glass.

A molten salt can be used as a vehicle for metallic ions. For examplethe molten bodies 33 may be of molten cuprous chloride clinging tocopper anode members 31. Cuprous ions enter the glass and the cuprouschloride is continuously replenished by reaction of chlorine released atthe anode members 31 with the copper of those members.

The anode structure 30 is suitably foraminous to enable the reducingatmosphere to permeate between adjacent anode members 31. For example.the anode members 31 may be supported from an openwork frame, asindicated diagrammatically at 35 in FIG. 2.

In a modified arrangement the anode members 31 may be individuallyconnected to separate current supply sources which supply current atdifferent voltages. For example the voltage of the supply to the firstanode member may be 1 volt with a progressive increase of l volt fromanode to anode. in some circumstances this ensures that the same currentflows from each of the molten bodies 33 into the glass surface.

Each of the anode members may be connected to its own transformer andrectifier circuit. Alternatively a single high current DC source is usedand a plurality of tappings on a potentiometer connected across thesource output provide theindividually regulatable voltages for theanodes.

Alternative arrangements may be employed in order to apply successiveelectrolytic treatments to the glass, each electrolytic treatment beingfollowed by an ion-reduction step. For example, instead of advancing theglass ribbon 25 continuously past the electrode structure 30, the glass,in sheet form or in the form of an article, may be held in a fixedposition and an electrode structure, reciprocated back and forth overthe surface of the glass to be treated, said surface being exposed to areducing atmosphere.

FIG. 3 illustrates such a process as applied to the treatment of ahollow glass half block 40. The block is supported on a molten metalbath 4!, for example of bismuth, which is connected to the negativeterminal of a direct current source 42. The upper surface of the halfblock, when floating on the bath 41, is to be treated by the method ofthis invention.

For this purpose an anode member 43 is disposed adjacent said uppersurface and B in electrical contact with said surface by way of a moltenanode body 44 which clings to the member 43. The member 43 is connectedto the positive terminal of the direct current source 42 and is mountedon a suitable carriage (not shown in the interests of clarity) forreciprocating movement parallel to the upper surface of the article 40,in the direction indicated by arrows X. A reducing atmosphere, forexample a hydrogen/nitrogen mixture, is maintained over the uppersurface of the article 40 by means of a suitable hood structure (notshown) similar to the hood structure 27 of F IG. 1.

in the illustrated example the anode member 43 comprises copper and themolten body 44 comprises bismuth. it will be apparent that as the member43 is reciprocated across the upper surface of the article 40, each zoneof this upper surface is subjected to a brief electrolytic action eachtime the molten body 44 passes across it followed immediately by anionreducing action due to the reducing atmosphere.

To achieve treatment of article 40 by the arrangement of FIG. 3approximately the same as the glass ribbon treatment described inexample ll above, a copper anode 43 having a thickness of 0.l25 inch inthe direction X of its reciprocating movement is reciprocated at anaverage speed of about 2 inches per second while a current of 50milliamps was passed through the anode 43 for a period of 30 seconds.The anode 43 has an effective width in a direction transverse to thedirection of reciprocation X of L5 inches and the total amplitude of thereciprocating movement is in this example 2 inches, so that an area ofl.5X2 square inches of the upper surface of the article 40 is treated.

As an alternative to reciprocation of the member 43 the article 40 andthe member 43 with its clinging body 44 could be rotated relatively toeach other about an axis perpendicular to the upper surface of thearticle 40. the anode member 43 extending in a radial direction withrespect to the axis of rotation. The anode member may be shaped as asegment having an angle of l radian thereby producing uniform treatmentof the article surface.

The bottom surface of a glass article can be treated by reversing thepolarity of the supply so that the molten metal bath 41 is electricallypositive. For example, the bath 4! may be of molten copper/bismuth alloyand. the article 40 reciprocated vertically or, where the article 40 isheld at a fixed position in the bath 4!, the bath metal may be pumped sothat its level rises and falls cyclically. This results in theelectrical contact with the bottom surface of the article beinginterrupted cyclically and contact of the bottom surface of the articleby reducing gas being established cyclically. so that the bottom surfaceacquires a highly concentrated surface layer of metallic copper.

As an alternative to the electrolytic treatments described above, theprocess according to the invention may be put into effect usingion-exchange from the vapor phase to introduce ions into a glass surfaceand then exposing the surface to a reducing atmosphere to reduce theions to the elemental metal. For example, exposure of the glass surfaceto silver bromide vapor would cause silver ions to be introduced intothe glass surface in exchange for sodium ions. By repeating theion-exchange and ion-reduction steps succesively a large number of timesa desired concentration of elemental metal can be built up in the glasssurface.

It will be appreciated that since metal is deposited in, rather, thanon, the glass surface by the method of the present invention theresulting metal layers or films are more durable than chemicallydeposited or vacuum-evaporated films on glass surfaces, and no specialprotection for the glass surface is necessary.

The present invention may be used to form fully or partially reflectingmetallic layers in glass surfaces. Where the metal deposited is suchthat it reflects infrared radiation preferentially, such as copper,glass results which is capable of preferentially rejecting infraredsolar energy.

Special effects can be obtained by subjecting the glass to treatmentwith more than one metal. A mixture of two different metals may bedeposited, for example by making alternate anode members 31 in FIG. I ofdifferent metals, or alternate layers of different metals may be formedby carrying out successive treatments in accordance with the inventionusing anodes of different metals.

We claim:

1. Method of manufacturing glass having a desired concentration ofelemental metal in its surface, comprising thermally conditioning theglass of a temperature at which it is susceptible to surfacemodification, imposing migration of metal ions into a region of theglass surface, immediately thereafter exposing that region to a reducingagent to reduce to elemental metal the metal ions which have migratedinto the glass surface, then imposing further migration of metal ionsinto that metal enriched surface region of the glass, again exposingthat region to a reducing agent to reduce to elemental metal the latestinflux of metal ions into the glass surface, said migration andreduction steps being repeated successively to build up a desiredconcentration of elemental metal in the glass surface.

2. A method according to claim 1, comprising contacting the glasssurface with a molten metal body, and connecting said body as an anodeto pass electric current between the body and the glass surface to causesaid ionic migration into the glass.

3. Method according to claim 2, comprising causing the molten metal bodyto cling to a metal locating member arranged adjacent the glass surface,and supplying the current to said member.

4. Method of manufacturing float glass having a desired concentration ofelemental metal in one face of the glass, comprising advancing floatglass in ribbon form along a bath of molten metal, contacting the uppersurface of the ribbon of glass with a plurality of molten metal bodiesextending transversely of the ribbon of glass, which bodies are spacedapart in the direction of advance of the glass, connecting each body asan anode to pass electric current between the bodies and the glassthereby enforcing ionic migration from each body into the upper surfaceof the ribbon and exposing the upper surface of the ribbon to a reducingatmosphere in the spaces between the molten metal bodies to reduce metalions in the glass surface to elemental metal which progressivelyaccumulates to the desired concentration as the glass advances beneaththe molten bodies.

5. Apparatus for the manufacture of glass having a desired concentrationof elemental metal in its surface. said apparatus comprising: meanssupporting glass to be treated at a temperature at which the glass issusceptible to surface modification; an anode including a body of moltenmetal to be introduced into the glassfwhich body has a surface inelectrical contact with a surface of the glass; an electrical currentsource connected to the anode and arranged to pass an electrolyticcurrent into a surface of the glass from said molten metal body; meansconfining a reducing atmosphere over said surface of the glass' andmeans effecting relative movement between the glass and the anode to subect each surface region of the glass to a succession of electrolyticsurface treatments by said molten metal, alternating with ion reductiontreatments by the reducing atmosphere 6. Method according to claim 2,comprising moving repetitively over each region of the surface of theglass to be treated, and reducing the metal ions in the glass surface byexposing the said surface to a reducing atmosphere between successivepassages of the molten metal body over each respective surface region.

7. Method according to claim 2, comprising moving the glass past aplurality of molten metal bodies contacting the glass and constitutingmolten metal anodes which are spaced apart in the direction of glassmovement, and supplying a reducing atmosphere into the spaces betweenadjacent anodes.

8. Apparatus according to claim 5, for the manufacture of flat glassribbon form, including a plurality of said anodes spaced apart in thedirection of ribbon advance, and wherein said support means comprisesmeans permitting advance of the glass in ribbon form at a controlledrate past said anodes in succession, the spaces between successiveanodes being filled with the reducing atmosphere.

9. Apparatus according to claim 8, for the manufacture of float glass,wherein the glass support means comprise a bath of molten metal, andwherein the anodes are mounted above the surface of said bath, themolten metal bodies contacting the upper face of the glass, andincluding means connecting the bath to the electrical current source tocomplete an electrolytic circuit for the treatment of the glass as itpasses beneath the anodes.

10. Glass having a concentration of elemental metal in its surface,produced by the method according to claim I.

11. Apparatus according to claim 8. for the manufacture of float glassincluding a tank structure containing a headspace and a bath of moltenmetal comprising said glass support means, and wherein said meansconfining a reducing atmosphere over said surface of the glass comprisesa hood structure in said headspace and surrounding said spaced apartanodes to substantially isolate the surrounded anodes from the remainderof said headspace.

12. Method according to claim I in which successive treatments arecarried out using different metals to build up a concentration of atleast two metals in the glass surface.

13. Method according to claim 2, in which the locating member is a metalbar which is soluble in the molten metal body.

* l i t UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3522 295 Dated November 23, 1971 Inventor(s) D. G. Loukes et a1 It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Change the title of the invention to read as follows:

--METHOD AND APPARATUS FOR PRODUCING SURFACE MODIFIED FLAT GLASS--.

Signed and sealed this 1st day of August 1972.

(SEAL) Attest:

EDw'ARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents USCOMM-DC B031 O-PGD i u s. GOVIRNMIN! rnnmno orncr nu o-qusu7 ORM PC1-1050 (10-69)

2. A method according to claim 1, comprising contacting the glasssurface with a molten metal body, and connecting said body as an anodeto pass electric current between the body and the glass surface to causesaid ionic migration into the glass.
 3. Method according to claim 2,comprising causing the molten metal body to cling to a metal locatingmember arranged adjacent the glass surface, and supplying the current tosaid member.
 4. Method of manufacturing float glass having a desiredconcentration of elemental metal in one face of the glass, compriSingadvancing float glass in ribbon form along a bath of molten metal,contacting the upper surface of the ribbon of glass with a plurality ofmolten metal bodies extending transversely of the ribbon of glass, whichbodies are spaced apart in the direction of advance of the glass,connecting each body as an anode to pass electric current between thebodies and the glass thereby enforcing ionic migration from each bodyinto the upper surface of the ribbon and exposing the upper surface ofthe ribbon to a reducing atmosphere in the spaces between the moltenmetal bodies to reduce metal ions in the glass surface to elementalmetal which progressively accumulates to the desired concentration asthe glass advances beneath the molten bodies.
 5. Apparatus for themanufacture of glass having a desired concentration of elemental metalin its surface, said apparatus comprising: means supporting glass to betreated at a temperature at which the glass is susceptible to surfacemodification; an anode including a body of molten metal to be introducedinto the glass; which body has a surface in electrical contact with asurface of the glass; an electrical current source connected to theanode and arranged to pass an electrolytic current into a surface of theglass from said molten metal body; means confining a reducing atmosphereover said surface of the glass; and means effecting relative movementbetween the glass and the anode to subject each surface region of theglass to a succession of electrolytic surface treatments by said moltenmetal, alternating with ion reduction treatments by the reducingatmosphere
 6. Method according to claim 2, comprising movingrepetitively over each region of the surface of the glass to be treated,and reducing the metal ions in the glass surface by exposing the saidsurface to a reducing atmosphere between successive passages of themolten metal body over each respective surface region.
 7. Methodaccording to claim 2, comprising moving the glass past a plurality ofmolten metal bodies contacting the glass and constituting molten metalanodes which are spaced apart in the direction of glass movement, andsupplying a reducing atmosphere into the spaces between adjacent anodes.8. Apparatus according to claim 5, for the manufacture of flat glassribbon form, including a plurality of said anodes spaced apart in thedirection of ribbon advance, and wherein said support means comprisesmeans permitting advance of the glass in ribbon form at a controlledrate past said anodes in succession, the spaces between successiveanodes being filled with the reducing atmosphere.
 9. Apparatus accordingto claim 8, for the manufacture of float glass, wherein the glasssupport means comprise a bath of molten metal, and wherein the anodesare mounted above the surface of said bath, the molten metal bodiescontacting the upper face of the glass, and including means connectingthe bath to the electrical current source to complete an electrolyticcircuit for the treatment of the glass as it passes beneath the anodes.10. Glass having a concentration of elemental metal in its surface,produced by the method according to claim
 1. 11. Apparatus according toclaim 8, for the manufacture of float glass including a tank structurecontaining a headspace and a bath of molten metal comprising said glasssupport means, and wherein said means confining a reducing atmosphereover said surface of the glass comprises a hood structure in saidheadspace and surrounding said spaced apart anodes to substantiallyisolate the surrounded anodes from the remainder of said headspace. 12.Method according to claim 1 in which successive treatments are carriedout using different metals to build up a concentration of at least twometals in the glass surface.
 13. Method according to claim 2, in whichthe locating member is a metal bar which is soluble in the molten metalbody.